A new route to the imidazole-2-thiones from 2-thiohydantoins. Implications in the study of ergothioneine.
1. 2-Thiohydantoins are reduced by borohydrides to 4(5)-hydroxyimidazolidine-2-thiones, which eliminate water in acid to form imidazole-2-thiones. Both steps take place in mild conditions, in high yield. A number of imidazole-2-thiones have been synthesized by this sequence of steps, with one, two or three substituents in the 1-, 3- and 4(5)-positions. 2. 4(5)-Hydroxyimidazolidine-2-thiones are ammonium pseudo-bases, giving rise to an equilibrium mixture of amino aldehyde, carbinolamine and mesomeric ammonium cationic forms. The elimination of water is suggested to be a property of the mesomeric ammonium cation. 3. The mild conditions in which imidazole-2-thiones are formed from 4(5)-hydroxyimidazolidine-2-thiones are similar to those in which ergothioneine, a naturally occurring imidazole-2-thione of uncertain function, is normally released and measured. It is suggested that the occurrence in vivo of a precursor to ergothioneine, in the form of a 4(5)-hydroxyimidazolidine-2-thione, would explain many otherwise conflicting published data.
D000447:Aldehydes; D001896:Boron Compounds; D055598:Chemical Phenomena; D002621:Chemistry; D004880:Ergothioneine / Q000096:biosynthesis*; D006827:Hydantoins; D007093:Imidazoles / Q000138:chemical synthesis*; D000644:Quaternary Ammonium Compounds; D013455:Sulfur; D014867:Water
D000447:Aldehydes; D001896:Boron Compounds; D006827:Hydantoins; D007093:Imidazoles; D000644:Quaternary Ammonium Compounds; D014867:Water; D013455:Sulfur; D004880:Ergothioneine